Re: Performance under contention

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Yeah, that was my concern, too, though Tom seems skeptical (perhaps
>> rightly). And I'm not really sure why the PROCLOCKs need to be in a
>> hash table anyway - if we know the PROC and LOCK we can surely look up
>> the PROCLOCK pretty expensively by following the PROC SHM_QUEUE.

> Err, pretty INexpensively.

There are plenty of scenarios in which a proc might hold hundreds or
even thousands of locks. pg_dump, for example. You do not want to be
doing seq search there.

Now, it's possible that you could avoid *ever* needing to search for a
specific PROCLOCK, in which case eliminating the hash calculation
overhead might be worth it. Of course, you'd still have to replicate
all the space-management functionality of a shared hash table.

regards, tom lane